fix(inspec): use the name `_mapdata` everywhere for coherency

test/integration/default/controls/_mapdata_spec.rb

   hostname: system.hostname
 }
 
-mapdata_file = "mapdata/#{system.platform[:finger].split('.').first}.yaml"
+mapdata_file = "_mapdata/#{system.platform[:finger].split('.').first}.yaml"
 mapdata_dump = inspec.profile.file(mapdata_file) % replacement
 
 control '`map.jinja` YAML dump' do